The goals of Project 1 are to design and evaluate new versions of SOSIP gp140 trimers based on a range of HIV- 1 genes and incorporating various sequence modifications intended to improve their structural, antigenicity and immunogenicity properties. The trimers designed in Project 1, with essential structure-based input from Project 2, will be produced by Core A, provided to Project 2 for structural studies, assessed for antigenicity and other properties within Project 1, and also sent to multiple external collaborators for additional research, including immunogenicity experiments in animals (which Project 1 will also be involved in analyzing). Project 1 will, therefore, be intimately involved inthe scientific program of the entire HIVRAD. Dr. John P. Moore, the PI of the HIVRAD, will direct Project 1, which will be based at the Weill Cornell Medical College (WCMC), New York. Dr. Moore will work closely with Dr. Rogier W. Sanders, who will lead a component at the Academic Medical Center, Amsterdam. The Specific Aims of Project 1 are: Aim 1: To improve the design of the currently most advanced SOSIP trimers, BG505 SOSIP.664, for structural and immunogenicity studies. We will design new SOSIP trimers using information from high-resolution x-ray and cryo-EM structures and animal immunogenicity studies. We will create variant trimers that target germline ancestors for bNAbs, and sequential trimers based on sequence evolution within infant-BG505. Other goals are to reduce trimer heterogeneity and thereby improve crystallization potential, mask non-NAb epitopes that may act as immunological decoys, better present bNAb epitopes to the immune system, and drive Ab evolution toward the development of bNAbs. Aim 2: To identify multiple SOSIP trimers from different genetic subtypes with properties comparable to BG505 SOSIP.664. We will combine our accumulated experience of trimer design, our knowledge of the properties of the BG505-based trimers (subtype A), and a bioinformatics approach, to identify and/or design new variants based on other subtypes, particularly B and C. The goals are to create a recipe that will enable us to make high quality SOSIP trimers from many/most genotypes and thereby expand the range of trimers available for vaccine- and structure-based studies in both Projects. Aim 3: To design and help evaluate immunogenicity studies using SOSIP trimers. The HIVRAD team has established collaborations with several groups, including but not limited to CHAVI-ID and IAVI, to provide trimer-based immunogens for animal immunization studies as part of the pathway towards human clinical trials. The Project 1 team will jointly design specific experiments with the relevan collaborators, with the involvement of the HIVRAD's Internal Steering Committee, and will contribute to the analysis of the studies by performing neutralization and related serology assays. RELEVANCE: The overall objective of this multi-site HIVRAD application is to help develop a preventative HIV-1 vaccine based on the induction of virus neutralizing antibodies by rationally designed, structurally relevant envelope glycoprotein trimers. Core A will make the SOSIP trimers designed in Projects 1 and 2, and provide them to both project teams and external collaborators. The goals of the application are highly relevant to public health and human welfare.